At which stage of the Krebs cycle does oxidative decarboxylation take place?

Explanation

The correct answer is option B, Step 3, where isocitrate is converted to α-ketoglutarate. This stage involves both oxidation and the release of carbon dioxide, fulfilling the definition of oxidative decarboxylation. The other options are incorrect because option A involves only isomerization, option C involves energy generation through substrate-level phosphorylation, and option D involves oxidation without carbon dioxide release.